In this proposed investigation, we will develop a prototype very high resolution MR- compatible SPECT system that will be installed inside a pre-existing 4.7 Tesla Varian MRI scanner and allows for very high resolution, simultaneous mouse brain imaging using both SPECT and MRI modalities. This system is optimized for very-high resolution simultaneous SPECT and MR imaging study of mouse brain. It would substantially benefit the on-going research at UIUC for developing immunotherapy for brain tumors. This MR-compatible SPECT system is based on a very high resolution imaging sensor based on a novel energy resolved photon counting (ERPC) hybrid pixel sensor that we are currently developing. Multiple detector modules are used in a stationary ring configuration, which allows a sufficient angular sampling without moving the SPECT system. In this R21 project, the prototype MR-compatible SPECT system consists of three ERPC detector modules, fitted inside the 33cm diameter bore of the Varian MRI scanner. The major design goals of this system are to allow simultaneous data acquisition and to offer comparable imaging resolution (250-400um from SPECT and 100-200 from MRI) with both modalities. The use of the semiconductor detector allows the use of multiple tracers, such as Tc-99m, I-125 etc, at the same time, which further improve the versatility of this SPECT/MRI dual-modality imaging system. This proposed R21 effort will be focused on (a) develop a triple-headed SPECT system, (b) integration of the SPECT system with an existing 4.7T MRI system and (c) evaluate the prototype dual modality system for phantom imaging studies. In particular, substantial efforts will be dedicated to minimize the interferences between the simultaneously operated SPECT and MRI systems. This proposed R21 investigation will be concluded by a design study for a complete MR-compatible very-high resolution SPECT system. PUBLIC HEALTH RELEVANCE: The very-high resolution MR-compatible SPECT system will be dedicated to in vivo SPECT/MRI dual-modality imaging. It offers very-high resolution images simultaneous acquired with both SPECT and MRI, will is proven to be important for brain caner study using mouse models. This development will substantially benefit the on-going research at UIUC on developing immunotherapy for brain tumors.